You’ve received lots of good advice from the comments above. A Voigtlander, Canon, or Nikkor 50mm lens in LTM would work very well on your M3. I also regularly shoot 40mm lenses on my M3, using the entire VF to frame. The Voigtlander Nokton 40mm f1.4 lens is quite good, compact, and can be had used at a reasonable price (I bought my multi-coated version used from the Head Bartender). The Minolta Rokkor-M 40mm f2.0 is excellent and comes in M-mount. The tiny (and recently discontinued) Voigtlander Heliar 40mm f2.8 is spectacularly good. So lots of choices if you want to go slightly wider than a 50.